Agile registration systems receive a mis-registered sheet at the input and deliver the sheet registered to a downstream “agile” registration datum, such as a photoreceptor or a drum. Typically, agile registration systems provide for approximately 2 or 3 degrees of movement between input and output. FIG. 1 shows an example of an agile registration system 10. In order to deliver the sheets downstream, the agile registration system 10 uses stationary nips 12, 14 to impart x-direction velocity vectors v0 (16) and v1 (18) on a sheet 20. The average of the velocity vectors 16, 18 (v1+v0)/2 provides an x-direction process direction) motion to the sheet. The difference between the velocity vectors 16, 18 (v1−v0) provides a rotation of the sheet 20. The sheet 10 is transported downstream and adjusted along a feed path 22 prior to entering a device.
When the sheet 20 enters the nips 12, 14 of the agile registration system 10, the velocities are set equal to the sheet velocity of the sheet 20 along the upstream feed path 22 to ensure correct hand-off between the sheet 20 and the upstream feed path 22 of the sheet 20. Agile registration begins after a sensor detects the sheet 20. The system 10 shown includes two lead edge sensors 24, 26 configured to report the time-of-arrival t0 and the process position x0 (28) and angle β0 (30) of the sheet 20. The system 10 further includes a lateral sensor 32 reports the lateral position y0 (34) of the sheet 20. In many cases, the lead-edge-center 28 or lead-edge-side 34 is considered the point that is being registered since simple geometric calculations may be used to yield values for the initial conditions of the registration point from sensor measurements.
To ensure the paper is delivered at the correct time and in the correct position, velocity profiles of both nips 12, 14 must be computed. The velocity profiles v1(t) and v0(t) at the a time, t=tf, and may be represented by xf, yf, and βf, with the velocity at the delivery location usually matching the velocity of the downstream device.
FIG. 2 (40) provides the system 10 with a sample trajectory 42 of the sheet 20 along the feed path 22 from arrival 44 of the sheet 20 at the nips 12, 14 during agile registration to the delivery 46 of the sheet 20 at the downstream device. Note, the trajectory of sheet 20 through the nip center 48 is curved, illustrating the correction to the position of the sheet 20 over time. The position of the sheet 20 is corrected to be in the proper lateral position by changing the lateral position and the skew of the sheet 20. As disclosed in U.S. Pat. No. 5,887,996 to Castelli et al., a skew in the sheet 20 results in both a skew error and lateral error. Hence, a lateral controller may be used to move the sheet 20 such that the skew error and lateral error are corrected.
Current strategies for sheet registration use sensors to take snap shots of the sheet as the agile registration begins, as shown on the trajectory as the arrival 44 of the sheet 20, to determine the appropriate location of the sheet at the delivery location, as shown on the trajectory as the delivery 46 of the sheet 20. The problem with such systems is that there is no verification or follow-up sensoring to ensure the sheet 10 really ends up at the delivery location in the correct position. When inaccuracies in any of the programmed inboard and outboard nip velocities and/or input sheet position result in registration errors in the process, lateral, and skew measurements. Thus, there is a need for a method of reducing the lateral error overtime using a single low-cost sensor.